feat: engagement page, engagement badge on client detail, stats API integration

- New Engagement page with score cards, distribution summary, sort/filter controls
- Score breakdown bars (recency, interactions, emails, events, notes)
- Engagement badge widget on ClientDetailPage with click-to-expand details
- Added Engagement to sidebar navigation with Zap icon
- API client methods for engagement scoring and stats overview

src/pages/ClientDetailPage.tsx

@@ -18,6 +18,7 @@ import EmailComposeModal from '@/components/EmailComposeModal';
 import ClientNotes from '@/components/ClientNotes';
 import LogInteractionModal from '@/components/LogInteractionModal';
 import MeetingPrepModal from '@/components/MeetingPrepModal';
+import EngagementBadge from '@/components/EngagementBadge';
 import type { Interaction } from '@/types';
 
 export default function ClientDetailPage() {
@@ -91,9 +92,12 @@ export default function ClientDetailPage() {
               {getInitials(client.firstName, client.lastName)}
             </div>
             <div className="flex-1 min-w-0">
-              <h1 className="text-2xl font-bold text-slate-900 dark:text-slate-100">
-                {client.firstName} {client.lastName}
-              </h1>
+              <div className="flex items-center gap-3">
+                <h1 className="text-2xl font-bold text-slate-900 dark:text-slate-100">
+                  {client.firstName} {client.lastName}
+                </h1>
+                <EngagementBadge clientId={client.id} />
+              </div>
               {client.company && (
                 <p className="text-slate-500 dark:text-slate-400">
                   {client.role ? `${client.role} at ` : ''}{client.company}